3. Copy YahooMessenger.exe from the archive you downloaded at step 1 into the location where you installed Yahoo Messenger 10, usually:
C:\Program Files\Yahoo!\Messenger (for Windows 32bit)

C:\Program Files (x86)\Yahoo!\Messenger(for Windows 64bit).

At this point we have completele deleted the ads from Yahoo Messenger. But:

DO NOT START YAHOO MESSENGER 10 YET!

4. Open Yahoo Tweaker.exe from the same downloaded archive. Check the "Enable multiple instances" checkbox. If you also want to change the startup animation, pick one from the list. Then, click the Apply button.